In artificial snowmaking, there are basically two types of systems which are presently used. The first is the "airless" system and the other is known as the "air" or "air/water" system. The airless snowmaking systems are so named because they use very little compressed air in the snowmaking processes. These systems typically have a housing with a fan mounted upstream of an ice nucleator and water nozzles. The nucleator provides ice nuclei which mix with the water droplets discharged from the nozzles and the airstream created by the fan carries the ice nuclei-water droplet mixture into ambient where ultimately snow like crystals are formed. The initial patents embodying this concept are U.S. Pats. Nos. 3,567,117, Eustis; 3,703,991, Eustis and Howell; 3,733,029, Eustis and Howell; and 3,774,842, Howell. Additional patents in this field embodying the basic airless snowmaking concepts are U.S. Pat. Nos. 3,948,442, Dewey; 3,979,061, Kircher; 4,083,492, Dewey; 4,105,161, Kircher; 4,222,519, Kircher; and 4,223,836, Eager.
The air or air/water snowmaking systems employ compressed air and water both of which are discharged simultaneously from a nozzle. The compressed air provides the motive force for discharging the nucleated water particles, which are formed upon discharge from the nozzle, into the ambient until they form snowlike crystals. U.S. Pat. No. 2,676,471, Pierce, Jr. illustrates the air/water snowmaking techniques. Also of interest are U.S. Pats. Nos. 2,968,164, Hanson and 3,964,682, Tropeano.
The airless systems have been found to be highly efficient machines when compared with the air/water systems. The airless systems have the ability to produce more snow with a given amount of energy than the air/water systems, and they can eliminate the high cost of installing the relatively large central air compressor station required for the air/water systems. However, the costs of the airless systems are higher than air/water systems per se, where the air/water system is purchased for a ski area with an existing compressed air source. Even though most ski areas recognize the energy saving advantages of the airless systems, many ski areas which have central air compressors have been reluctant to install an airless system for a number of reasons. They do not want to install the large electrical distribution systems necessary for electrically powered airless systems or haul fuel for internal combustion engine powered airless systems. They do not have the terrain on which the large airless system snowmaking machines can be moved or the equipment to move them with or they do not have the cold ambient temperatures that make airless sytems most economical. Lastly, they do not want to abandon use of the compressed air station.
A third type of system has been proposed which is broadly described in U.S. Pat. No. 3,945,567, Rambach. This system purports to combine features of both the airless and air/water systems. It provides for the separate formation of ice nuclei and water droplets. An air motor powered by compressed air drives a fan, dispensing with the need for electrical power or power from an internal combustion engine. This system allows ski areas which are already equipped for the air/water systems to substitute this system for the conventional air/water systems. As a practical matter the systems using air motors to drive a fan have operational difficulties. The expansion and shaft work of the air in the motor results in the cooling of the air well below the freezing point of water. Since compressed air usually contains water vapor, formation and deposition of ice takes place which then renders the air-motor inoperative.
The present invention is directed to a system for snow making which system uses the nucleator, water droplet, fan concept of the airless systems and is powered by compressed air. The system avoids the difficulties of icing or freeze up of the fan by the use of a reaction fan. The reaction fan discharges its compressed air from the tips of the blades (external air jet reaction) in free space within the housing downstream of the fan. The system enhances the efficiency of snowmaking particularly at higher temperatures (26.degree.-32.degree. F.), by creating a flow of supercooled (i.e. subfreezing) air, in the region of the ice nuclei-water droplet discharge.
The method of my invention includes creating in separate zones ice nuclei and water droplets, generating a supercooled airstream by the expansion of compressed air and flowing the supercooled airstream into the region wherein the ice nuclei and the water droplets commingle to form an ice nuclei-waterdroplet mixture. The mixture is discharged to ambient whereby snowlike crystals are formed.
The apparatus of the invention broadly comprises a nucleator to provide for the generation of ice nuclei which is spaced apart from water nozzles for the creation of water droplets. Means to create an airstream by the discharge of compressed air is provided with results in a supercooled airstream which flows and contacts the ice nuclei-water droplet.
More particularly in the present invention a reaction fan driven by compressed air is used. The expansion of the compressed air discharged from the reaction jets takes place in essentially free space within the housing the result being that the ice particles formed upon discharge of the compressed air are carried away in the airstream without difficulty. This allows use of an air driven fan in snowmaking which avoids the problems of freeze up and further provides for a supercooled airstream within the housing and in the region if discharge of the water droplets and ice nuclei for enhanced snowmaking efficiency. Additionally a source of ice nuclei are provided in addition to those created by the nucleator.
It is well understood that in snowmaking it is necessary to vary the flow of the water depending primarily upon the temperature at which the snow is made. This is commonly achieved by putting valves on at least some of the nozzles which produce the water droplets. If a nozzle which is facing upwardly, (such as a nozzle on the lower half of a manifold ring) is shut off with a valve behind the nozzle, typically some water will remain in the nozzle which will freeze and disable the nozzle from further use.
The airless systems use electric heaters to obviate this problem. Our invention further provides for a valve system which is designed to avoid the problems of freeze up without relying on thermal energy from an independent source to prevent the freeze up.